Guardians approve lake drawdown changes

Otago Daily Times

2 days ago

Approved changes to operating guidelines for hydro-electricity generation at Lake Manapouri will not cause unnatural variations of lake levels, the Guardians of Lakes Manapouri, Monowai and Te Anau say.
Fears have been raised that using too much water when lake levels are low could cause permanent damage to the lake's shoreline.
However, Guardians chairman Darryl Sycamore said the approved changes to the "drawdown rate" only applied to the upper range of low lake levels.
Critically, the changes the Guardians had approved mimicked drops in lake levels previously observed in the natural record.
"The Guardians have considered a range of proposals from Meridian Energy and have agreed to some amendments which mimic variations in the natural record of lake level prior to the establishment of the Manapouri hydro-scheme," Mr Sycamore said.
"These amendments will enable additional energy generation and provide resilience of our electricity network."
The Guardians were mandated in the Conservation Act to have particular regard to the effects of the operation of the hydro scheme on social, conservation, recreation and tourism values, he said.
"We have carefully considered the proposed amendments on the values prescribed in the Act and have only provided our support to those which will likely result in less than minor effects," he said.
If further changes were sought, unless Meridian could provide robust scientific reasoning to adopt the changes, they would not have the Guardians' support.
Lake Manapōuri and Lake Te Anau had "given enough to NZ Inc" and any additional energy would have to be produced elsewhere, he said.
Energy Minister Simon Watts heralded the changes as a "boost" to New Zealand's hydro generation and energy security.
They would allow an extra 45GWh of energy to be produced by the Manapōuri Power Scheme each year — enough energy to power about 6000 homes, Mr Watts said.
"Last winter, New Zealand faced an energy shortage that led to significant price increases for consumers, in part due to low hydro lake levels," he said.
"This government will not accept a repeat of last winter and is working at pace to ensure we have a reliable and affordable energy supply.
"Lake Manapōuri and Lake Te Anau are not only environmentally and culturally significant, but they are also essential to New Zealand's energy system."
The changes balanced the needs of New Zealand's electricity system with the environmental impact on the lakes and their surrounding areas, he said.
Emeritus Professor Sir Alan Mark, of Dunedin, the first chairman of the Guardians, said changes to the low operating range risked damage to shorelines, or the loss of beaches that had taken "eons" to develop.
"They're not going to be replaced if they're lost," Sir Alan said.
When lake levels were lowered to unnatural levels in 1972 — the year before the Guardians were established — several beaches were lost forever, Sir Alan said.
Decades of daily lake level data was used to establish the guidelines more than 50 years ago and they had since "proved to be extremely successful" in retaining the lakes' beaches in their natural state, he said.
Meridian manages about half of New Zealand's total hydro storage and uses Lakes Pūkaki, Ōhau, Aviemore, Waitaki, Benmore, Manapōuri and Te Anau to generate energy.
Previously, a Meridian spokesman said the government "has been very clear in its desire to ensure there's enough electricity for all New Zealand homes and businesses this winter, and Manapōuri Power Station has an important role to play in that".
Changes to the operating guidelines include changing the drawdown rates, reducing duration requirements on how long the lakes can stay within the first band of low operating ranges, and removing equinoctial requirements, which set additional limits on how hydro generation could affect the lakes twice a year during windier periods.
[e-mail]